Pseudodynamic off-chip driver calibration

Abstract

A driver system, a driver calibration circuit arrangement for calibration of an impedance of a driver circuit arrangement, and a method for calibration of an impedance of a driver circuit arrangement can achieve improved driver behavior, with respect to undesirable distortions of the slew rate caused by off-chip drivers of DDR memory modules. A driver system has a first driver part with at least one variable impedance by which an operating point of the first driver part is determined with respect to a first potential and a second potential. The potentials supply the first driver part. A first monitoring device adjusts an impedance value of the variable impedance such that the operating point differs from a mid-point of the first and of the second potential.

1. A driver calibration circuit arrangement for calibration of an impedance of a driver circuit arrangement connected between a first potential and a second potential, the driver circuit arrangement having a predetermined operating range over only a portion of a range between the first and second potentials, the driver calibration circuit arrangement comprising:
 a circuit arrangement with a variable impedance; 
 a reference impedance connected to the circuit arrangement; and 
 a monitoring device for sequentially varying the impedance of the circuit arrangement with the variable impedance until the potential at a junction point between the reference impedance and the circuit arrangement with the variable impedance equals a mid-point of the predetermined operating range, wherein the mid-point of the predetermined operating range differs from the mid-point between the first and the second potentials. 
 
   
   
     2. The driver calibration circuit arrangement as claimed in  claim 1 , wherein the mid-point of the predetermined operating range differs from the mid-point between the first and the second potential by more than 15% of the difference between the first and the second potential. 
   
   
     3. The driver calibration circuit arrangement as claimed in  claim 1 , wherein the mid-point of the predetermined operating range differs from the mid-point between the first and the second potential by less than 35% of the difference between the first and the second potential. 
   
   
     4. The driver calibration circuit arrangement as claimed in  claim 1 , wherein the mid-point of the predetermined operating range differs from the mid-point between the first and the second potential by 20% of the difference between the first and the second potential. 
   
   
     5. The driver calibration circuit arrangement as claimed in  claim 1 , wherein the driver circuit arrangement is a pull-up amplifier. 
   
   
     6. The driver calibration circuit arrangement as claimed in  claim 1 , wherein the driver circuit arrangement is a pull-down amplifier. 
   
   
     7. A system, comprising:
 a driver circuit arrangement connected between a first potential and a second potential, the driver circuit arrangement having a predetermined operating range over only a portion of a range between the first and second potentials; 
 a driver calibration circuit arrangement; 
 a circuit arrangement with a variable impedance; 
 a reference impedance connected to the circuit arrangement; and 
 a monitoring device for sequentially varying the impedance of the circuit arrangement with the variable impedance until the potential at a junction point between the reference impedance and the circuit arrangement with the variable impedance equals a mid-point of the predetermined operating range, wherein the mid-point of the predetermined operating range differs from the mid-point between the first and the second potentials. 
 
   
   
     8. The system as claimed in  claim 5 , wherein the system is a GDDR3 memory chip. 
   
   
     9. A method for calibration of an impedance of a driver circuit arrangement connected between a first potential and a second potential, the driver circuit arrangement having a predetermined operating range over only a portion of a range between the first and second potentials, the method comprising:
 providing a calibration circuit comprising a circuit arrangement with a variable impedance coupled to a reference impedance; and 
 sequentially varying of the impedance of the circuit arrangement with a variable impedance until the potential at a junction point between the reference impedance and the circuit arrangement with the variable impedance equals a mid-point of the predetermined operating range, wherein the mid-point of the predetermined operating range differs from the mid-point between the first and the second potentials. 
 
   
   
     10. The method as claimed in  claim 9 , wherein the mid-point of the predetermined operating range differs from the mid-point between the first and the second potential by more than 15% of the difference between the first and the second potential. 
   
   
     11. The method as claimed in  claim 9 , wherein the mid-point of the predetermined operating range differs from the mid-point between the first and the second potential by less than 35% of the difference between the first and the second potential. 
   
   
     12. The method as claimed in  claim 9 , wherein the mid-point of the predetermined operating range differs from the mid-point between the first and the second potential by 20% of the difference between the first and the second potential. 
   
   
     13. The method as claimed in  claim 9 , wherein the driver circuit arrangement is part of a memory system. 
   
   
     14. A driver calibration circuit for calibrating an impedance of a driver circuit connected between a first potential and a second potential, the driver calibration circuit comprising:
 a variable impedance circuit coupled to a reference impedance at a node; and 
 a monitoring device configured to vary an impedance of the variable impedance circuit until a potential at the node substantially equals a calibration potential for the driver circuit, the calibration potential being different from a mid-point between the first and second potentials, wherein the monitoring device is further configured to calibrate the impedance of the driver circuit in accordance with the impedance of the variable impedance circuit corresponding to the calibration potential. 
 
   
   
     15. A system, comprising:
 the driver calibration circuit of  claim 14 ; and 
 the driver circuit. 
 
   
   
     16. A driver calibration circuit for calibrating an impedance of a driver circuit comprising first and second branches connected in series between first and second supply potentials, the driver calibration circuit comprising:
 a first reference voltage divider comprising a variable impedance circuit coupled to a first reference impedance at a first node; 
 a second reference voltage divider comprising a variable impedance circuit coupled to a second reference impedance at a second node; and 
 a monitoring device configured to sequentially varying the impedance of the variable impedance circuit of the first reference voltage divider until the potential at the first node substantially equals a first calibration potential, and to sequentially varying the impedance of the variable impedance circuit of the second reference voltage divider until the potential at the second node substantially equals a second calibration potential, the first and second calibration potentials being different from the mid-point between the first and the second potentials, 
 wherein the monitoring device is further configured to calibrate the impedance of the first branch of the driver circuit in accordance with an impedance which produced the first calibration potential at the first node, and to calibrate the impedance of the second branch of the driver circuit in accordance with an impedance which produced the second calibration potential at the second node. 
 
   
   
     17. The driver calibration circuit of  claim 16 , wherein the first branch is a pull-up branch and the second branch is a pull-down branch. 
   
   
     18. The driver calibration circuit of  claim 16 , wherein:
 the first branch of the driver circuit operates over a first range which is a portion of a range between the first and second potentials and the second branch of the driver circuit operates over a second range which is a portion of the range between the first and second potentials; and 
 the first calibration potential is a midpoint of the first range and the second calibration potential is a midpoint of the second range. 
 
   
   
     19. A system, comprising:
 the driver calibration circuit of  claim 16 ; and 
 the driver circuit.